Cardiac resynchronization therapy (CRT) resynchronizes the electrical activation and therefore the contractions of the heart's chambers to enhance pumping efficiency. Benefits may include increased exercise capacity and reduced hospitalization and mortality. CRT devices operate by controlling or affecting the timing of contraction of one or more cardiac chambers relative to one or more other cardiac chambers. For example, contractions of one or more of the ventricle(s) may be timed relative to contraction of the atria, or contractions of the left and right ventricles may be timed relative to one another.
A “fusion” beat occurs when multiple activation signals affect the same tissue at the same time. For example, electrical fusion between pacing of one ventricle with spontaneous activation of another ventricle (for example, paced left ventricular activation and spontaneous right ventricular activation) produces a fusion beat. The generation of fusion beats is a goal of cardiac resynchronization in many circumstances.
Prior systems generally included intracardiac electrodes coupled via transvenous leads to an implanted pulse generator. The leads of such systems are widely known as introducing various morbidities and are prone to eventual conductor and/or insulator failure. The presence of leads and their known morbidities and failures in CRT systems likely reduce usage within the indicated population of heart failure patients.
Newer generation pacemakers include the leadless cardiac pacemaker (LCP), which can be implanted entirely within the heart and does not require a transvenous (or any) lead. Such devices are commercially available in certain placed, but are currently indicated for use in bradycardia pacing. The LCP also presents an opportunity to provide an alternative to traditional CRT therapy using transvenous leads. New and alternative systems, devices and methods directed at providing CRT therapy using the LCP are desired.